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<h2>Most Widely Deployed SQL Database</h2>

<p>We <em>believe</em> that there are more copies of SQLite
in use around the world than any other SQL database engine,
and possibly all other SQL database engines combined.  We cannot
be certain of this since we have no way of measuring either
the number of SQLite deployments nor the number of deployments
of other databases.  But we believe the claim is defensible.</p>

<p>The belief that SQLite is the most widely deployed SQL
database engine stems from its use as an embedded database.
Other database engines, such as MySQL, PostgreSQL, or Oracle,
are typically found one to a server.  And usually a single
server can serve multiple users.  With SQLite, on the other
hand, a single user will typically have exclusive use of
multiple copies of SQLite.  SQLite is used on servers, but
it is also used on desktop PC, and in cellphones, and PDAs,
and MP3-players, and set-top boxes.</p>

<h3>Estimates</h3>

<p>At the end of 2006, there were 100 million websites on the internet.
<a href="http://news.netcraft.com/archives/2006/11/01/november_2006_web_server_survey.html">&#91;1]</a>
Let us use that number as a proxy for the number of deployed
SQL database engines other than SQLite.  Not every website
runs an SQL database engine and not every SQL database engine
runs a website.  Larger websites run multiple
database engines.  But the vast majority of smaller websites
(the long tail) share
a database engine with several other websites,
if they use a database engine at all.
And many large SQL database installations have nothing to do with
websites.
So using the number of websites as a surrogate for the number of operational
SQL database engines is a crude approximation, but it is the best
we have so we will go with it.  (Readers are encouraged to submit
better estimates.)</p>

<p>Now let's consider where SQLite is used:</p>

<ul>
<li>300 million copies of Mozilla Firefox.</li>
<li>20 million Mac computers, each of which contains multiple
copies of SQLite</li>
<li>20 million websites run PHP which has SQLite built in.  
<a href="http://www.php.net/usage.php">&#91;3]</a>  We have no
way of estimating what fraction of those sites actively use
SQLite, but we think it is a significant fraction.</li>
<li>450 million registered <a href="http://www.skype.com/">Skype</a> users.</li>
<li>20 million Symbian smartphones shipped in Q3 2007
<a href="http://www.symbian.com/news/pr/2007/pr20079552.html">&#91;5]</a>
Newer versions of the SymbianOS have SQLite built in.  It is unclear
exactly how many Symbian phones actually contain SQLite, so we will
use a single quarter's sales as a lower bound.</li>
<li>10 million Solaris 10 installations, all of which require SQLite in
order to boot.</li>
<li>Millions and millions of copies of
<a href="http://www.mcafee.com/">McAfee</a> anti-virus software all
use SQLite internally.</li>
<li>Millions of iPhones use SQLite</li>
<li>Millions and millions of other cellphones from 
manufactures other than Symbian and Apple use SQLite.
This has not been publicly acknowledged by the manufactures
but it is known to the SQLite developers.</li>
<li>There are perhaps millions of additional deployments of
SQLite that the SQLite developers do not know about.</li>
</ul>

<p>
By these estimates, we see at least 500 million SQLite deployments
and about 100 million deployments of other SQL database engines.  These
estimates are obviously very rough and may be off significantly.  
But there is a wide margin. So the SQLite
developers think it is likely that SQLite is the most widely deployed
SQL database engine in the world.
</p>

